Like PMS, Pre Menstral Syndrome, Instead, Pre Eating Syndrome. When you are in a shitty mood because you havent eaten for too long. As a woman is in a bad mood when she has PMS because she hasnt had her period in too long.

PES stands for Phonetics and English speaking, an insanely useless class that is a must take for any student wishing to rot his/her way to glory because of the induced boredom, in a well known institute in western india.
Pronunciation: like 'Piss' ( At least it _should_ be like that)
feeling after attending the class: Like Piss; disgusting, but a feeling of relief after its over.